In this article we show that verbo-nominal expressions be on the/one’s way/road emerged as lexical composite predicates in Old English. These templates came to be elaborated by directional adjuncts, adjuncts describing states or events, and purpose clauses. In Late Modern English, the structure with a to-infinitive was functionally reinterpreted as a secondary auxiliary + lexical head, whose core sense is imminential aspect. On the basis of this case study, we develop a theoretical reflection on the differences between lexicalization and grammaticalization, as they emerge within a functional-constructional approach. On the syntagmatic axis, we adopt Boye & Harder’s (2007, 2012) principles for distinguishing lexicalized from grammaticalized uses on the basis of their having primary or secondary status in discourse usage. On the paradigmatic axis, we rethink the neo-Firthian distinction between lexis and grammar in diachronic terms. Individual lexical items are defined by their collocations (Sinclair 1991) and grammatical values by their systemic interdependencies (Halliday 1992). Lexicalization is then characterized by the development of distinctive collocational networks and grammaticalization by the acquisition of the defining interdependencies with values from related grammatical systems.